RNA interference refers to the process of sequence-specific post-transcriptional gene silencing in animals that is mediated by small inhibitory nucleic acid molecules (siRNAs) a double-stranded RNA (dsRNA) that is homologous in sequence to a portion of a targeted messenger RNA. See Fire, et al., Nature 391:806, 1998, and Hamilton, et al., Science 286:950-951, 1999. These dsRNAs serve as guide sequences for the multi-component nuclease machinery within the cell that degrade the endogenous-cognate mRNAs (i.e., mRNAs that share sequence identity with the introduced dsRNA).
The process of post-transcriptional gene silencing is thought to be an evolutionarily-conserved cellular defense mechanism used to prevent the expression of foreign genes and is commonly shared by diverse flora and fauna. Fire, et al., Trends Genet. 15:358, 1999. Such protection from foreign gene expression may have evolved in response to the production of double-stranded RNAs (dsRNAs) derived from viral infection or from the random integration of transposon elements into a host genome via a cellular response that specifically destroys homologous single-stranded RNA or viral genomic RNA.
RNAi has been studied in a variety of systems. Fire et al. were the first to observe RNAi in C. elegans. Nature 391:806, 1998. Bahramian & Zarbl and Wianny & Goetz describe RNAi mediated by dsRNA in mammalian systems. Molecular and Cellular Biology 19:274-283, 1999, and Nature Cell Biol. 2:70, 1999, respectively. Hammond, et al., describes RNAi in Drosophila cells transfected with dsRNA. Nature 404:293, 2000. Elbashir, et al., describe RNAi induced by introduction of duplexes of synthetic 21-nucleotide RNAs in cultured mammalian cells including human embryonic kidney and HeLa cells. Nature 411:494, 2001.
To date, siRNA is an emerging novel field with significant clinical implications. However, the technology is hampered by a number of limitations, such as difficulty and impracticality of its delivery in vivo. Although viral vector-based siRNA delivery systems have been widely used, their specificity and safety remains significant issue. While delivery of nucleic acids offers advantages over delivery of cytotoxic proteins such as reduced toxicity prior to internalization, there is a need for high specificity of delivery, which is currently unavailable with the present systems.
The benefits of preventing specific protein production in mammals include the ability to treat disease caused by such proteins. Such diseases include those that are caused directly by such a protein such as multiple myeloma and Waldenstrom's macroglobulinemia which are caused by harmful concentrations of a monoclonal immunoglobulin as well as diseases in which the protein plays a contributory role such as the effects of inflammatory cytokines in asthma.
Introduction of dsRNA into mammalian cells induces an interferon response which causes a global inhibition of protein synthesis and cell death. However, dsRNA several hundred base pairs in length have been demonstrated to be able to induce specific gene silencing following cellular introduction by a DNA plasmid (Diallo M et al. Oligonucleotides 2003).
Waldenström's macroglobulinemia remains an incurable and fatal disease. The manifestations of this disease that are due to high concentrations of monoclonal IgM are hyperviscosity and systemic amyloidosis which may result in death.
Thus, there exists a need to develop a treatment for Waldenström's macroglobulinemia based on siRNA.